The present invention relates to a data transfer method for executing data read/write in a system wherein a center and a target machine are connected by a network.
In the prior art, a center and an individual target machine are connected in a point-to-point fashion using a telephone line, and communication is effected therebetween to execute data write/read.
However, even if there is information to be sent from the target machine, the center has a main right of control, and immediate communication is not effected. The information can first be sent after line connection is established from the center.
In the prior-art method as described above, data read/write is performed using the telephone line, and thus the communication speed varies depending on a modem. For instance, the communication speed is between ten-odd KBPS and several-ten KBPS and is slow. Thus, a considerable length of time is consumed.
Since the communication speed is slow, the call time increases, and a high cost is incurred due to the use of the telephone line.
Moreover, since the telephone line is an analog line, the probability of communication error is high. There may be a problem that the communication is interrupted, and thus communication has to be established once again, or a still longer time is needed owing to an erroneous procedure.
Besides, since the center has a main right of access, information from the target machine is not immediately told to the center, and real-time operations cannot be performed.
In order to solve the problem, there is an idea that a dial call is made from the target machine. In this case, however, since the user's line is used without permission, a communication cost occurs on the user side. In addition, a call cannot be made in the case of a dedicated receiving line.
There is another idea of using the Internet for the network. However, in most cases, an Intranet in a company is provided with a firewall for preventing access from the outside, and an external data access is substantially prohibited.